Allen is already contracted until 2020, but his new two-year deal is a reward from his strong start to the season.
“I’m really excited to sign with the club until the end of 2022. I love the club and I love the people at the club,” Allen told the club’s website.
“They’ve been so welcoming of me in my first 18-months at the club and I couldn’t wait to extend.
“As a young kid, I just want to focus on playing the best footy I can and helping the club in any way possible, so to get this done was a big milestone for me.
“Now I can just try to play some good footy and help the team any way I can.”
Allen has played five games over the past two seasons for six goals, including all three matches in 2019.